The HIV Preclinical Vaccine Development Master Agreement Program is intended to make it possible for the NIAID to respond rapidly and efficiently to provide resources to evaluate candidate vaccines, accelerate the development of promising vaccine approaches, and answer basic questions directly related to vaccine development. This Program complements other NIAID-supported projects and provides the NIAID with resources to complement both basic and applied research in order to accelerate efforts aimed at development and licensing of safe and effective AIDS vaccines. The Contractor (ABL) will compare the immunogenicity and efficacy of a variety of configurations of the envelops of primary HIV-1 isolates to determine if the actual physical structure of the envelop and the epitopes of the envelope exposed to the immune system can affect the immune responses to the proteins. The contractor will provide various configurations of one or more primary HIV-1 envelopes: e.g. (1) monomeric gp120, (2) "oligomeric" envelope with gp120-gp41 cleavage site intact or deleted, (3) gp120-CD4 complexes and (4) others. These products may subsequently be used as reagents in laboratory investigations and as components of candidate vaccines to be evaluated for immunogenicity in non-human primates.